Reciprocating pumps are those which cause the fluid to move using one or more oscillating pistons, plungers or membranes (diaphragms), and restrict motion of the fluid to the one desired direction by check valves. One type of reciprocating pump is a diaphragm pump. A diaphragm pump is a positive displacement pump that uses a combination of the reciprocating action of a diaphragm, such as a rubber diaphragm, a wobble plate for driving each of a series of pistons formed in the diaphragm, a series of chambers formed on a valve housing for receiving piston structures of the diaphragm, and suitable non-return check valves coupled to the valve housing to ultimately pump a fluid from an inlet port to an outlet port.
Diaphragm pumps are commonly used to move relatively small amounts of fluid, such as water from one location to another. Diaphragm pumps can be used, for example to move water into and out of a recreational vehicle, on property, and the like. Typical flow rates for diaphragm pumps are up to ten gallons per minute (GPM) for commercial applications, although diaphragm pumps with greater flow capacities are available for industrial applications.
Diaphragm pumps are often driven by motors, gas-powered or electric motors including a drive shaft. A cam and ball bearing assembly interposed between the drive shaft and a wobble plate convert the rotational movement of the drive shaft to the push-pull motion of a series of pistons through the wobble plate. The wobble plate is mechanically coupled to the diaphragm. A nutating action of the diaphragm and wobble plate acts to actuate each piston sequentially into each chamber of the series of chamber defined on the valve plate to push and pull fluid into and out of each chamber.
Diaphragm pumps are typically single-acting in which suction during one direction of piston motion pulls fluid from in inlet chamber into a chamber of the valve plate, and during the other direction of the piston motion discharges the fluid from the chamber into an outlet chamber. More specifically, when the volume of a chamber of valve plate is increased (i.e. the piston moving out of or away from the chamber), the pressure in the chamber decreases, and fluid is drawn into the chamber from the inlet chamber in fluid communication with the inlet port to the pump. When the chamber pressure later increases from decreased volume (the piston moving into or down the chamber), the fluid previously drawn into the chamber is forced out of the chamber into an outlet chamber in fluid communication with an outlet port of the pump. Finally, the diaphragm moving up and out of the chamber once again draws fluid into the chamber, completing the cycle.
Examples of diaphragm pumps are described in, for example, U.S. Pat. Nos. 5,791,882, 6,048,183, 6,623,245, and 6,840,745 all of which are incorporated herein by reference in their entireties.
As discussed above, the wobble plate is operably coupled to the rotating drive shaft of a motor via the cam/bearing assembly. More particularly, the cam is coupled the drive shaft at an inner surface of the cam such that the cam does not rotate with respect to the shaft, but rather with the shaft. The cam also includes an outer annular surface coupled to an inner race of the ball bearing such that the cam does not rotate relative to the inner race of the ball bearing. The wobble plate is coupled to an outer race of the ball bearing such that the wobble plate surrounds the cam/bearing assembly, and the wobble plate does not rotate with respect to the outer race of the ball bearing.
During pump operation, particularly continuous duty operation, heat is generated from internal friction in the bearing as well as radiant heat from the motor. The generated heat causes the connections between the cam and bearing, and the wobble plate and bearing to become loose due to different expansion rates of the materials forming each of the cam, bearing, and wobble plates. When the connections become loose, flow performance suffers, such that flow can be reduced in excess of 50% of its capability. More heat from friction is generated after the connections become loose, accelerating the performance decrease and ultimately causing the bearing to fail.
Another common mode of failure of either the connections between the cam and bearing or the bearing and wobble plate are caused from the offset positioning of the cam on the drive shaft of the motor. The nutating action then places excessive load on the wobble plate which can dislocate the wobble plate from the bearing and/or the cam. Harmonic oscillations created due to the offset nature of the wobble plate can also cause the bearings to come loose. Similar to above, when the connections become loose, flow performance suffers, such that flow can be reduced in excess of 50% of its capability.
One technique for lengthening the durability of a cam/bearing connection 1 and referring to FIG. 1, is to press fit a cam 10 made of cast zinc allow into an inner race 14 of a bearing 12 forming an interference fit. Cam 10 can be staked into place for further durability by punching dimples 16 into a face 18 of cam 10 as shown in FIG. 1, thus deforming cam 10 to help hold it into bearing 12. Although staking cam 10 into bearing 12 has improved the durability of the connection, failures are still seen after long continuous duty operation.
Regarding a wobble plate/bearing connection 20 as shown in FIG. 2, during assembly, a wobble plate 22 made of cast aluminum alloy is heated to 140 degrees Celsius and bearing 12 is pressed into wobble plate 22. Because wobble plate 22 is machined to tight tolerances, after wobble plate 22 cools and shrinks, there is a tight interference fit between an outer race 28 of bearing 12 and wobble plate 22. Wobble plate 22 is then staked at 24 to further secure bearing 12 to wobble plate 22 as shown in FIG. 2. Further, a plurality of set screws 26 are installed to hold outer race 28 of bearing 12 from rotating inside wobble plate 22. This technique has greatly reduced or even completely eliminated the loose connection condition between the wobble plate and bearing even after 1000+ hours of continuous duty operation. However, this technique is both expensive and time consuming during assembly.
Regarding the check valve and valve housing assembly, inlet and outlet valves positioned on and carried by the valve housing typically found in diaphragm pumps have problems of inconsistent sealing, thereby further reducing the pump operation efficiency.
Referring to FIGS. 3A-4B, a prior art inlet valve 30 includes a central mounting section 32, such as a post, and a resilient, seal-forming section 34 surrounding an end 36 of post 32. Central mounting section 32 acts to secure inlet valve 30 within a valve seat 38 of a chamber of the valve housing. Resilient section 34 includes a center section 40 and a peripheral relief zone 42 or lip. Peripheral relief zone 42 acts to form a seal when slightly flexed within valve seat 38 of the valve housing, thereby sealing and restricting fluid communication through the inlet apertures.
Referring to FIGS. 4A-4C, prior art valve is depicted being mounted in a valve seat of a chamber of the valve housing. Referring to FIG. 4A, a first side 44 of peripheral relief zone 42 is shown in the relaxed position, i.e. how the valve naturally lies prior to being assembled within the valve seat, while a second side 46 is shown in a slightly flexed, sealed position, i.e. when the piston of the diaphragm is moving into the chamber in which the inlet valve is mounted such that fluid flow is restricted or completely prevented. As shown in FIG. 4C, a first side 44 of peripheral relief zone 42 is again shown in the relaxed position, i.e. how the valve naturally lies prior to being assembled within the valve seat, while a second side 47 is shown in a flexed, or opened position, such that peripheral relief zone 42 is significantly flexed or lifted out of the seat to allow fluid flow. As shown in FIG. 4A, a cross-section of the peripheral relief zone comprises a stepped portion or a mathematical profile represented by a discrete or discontinuous function. However, this “stepped” design provides minimal flexural relief in that it only seals along an edge of lip 42, such that an effective sealing area 48 of valve 30 is limited to a thin line (as seen on side 46), creating sealing inconsistencies.
Referring to FIGS. 5A-6B, a prior art outlet valve 50 includes a central mounting section 52, such as a post, and a resilient, seal-forming section 54 surrounding an end of post 52. Central mounting section 52 acts to secure outlet valve 50 within a valve seat 56 on an exterior side of the valve housing such that outlet valve 50 extends between two chambers of the valve housing. Resilient section 54 includes a center section 58 and a peripheral relief zone or lip 60. Peripheral relief zone 60 acts to form a seal within the valve housing, thereby sealing and restricting fluid communication from a chamber through the outlet apertures, i.e. when a piston of the diaphragm is moving out of the chamber.
Referring to FIGS. 6A and 6B, prior art outlet valve 50 is depicted being mounted in a valve seat 56 on an exterior of the valve housing such that outlet valve covers outlet apertures of a chamber of the valve housing. A first side 62 of peripheral relief zone 60 is shown in the relaxed position, i.e. how the valve naturally lies prior to being assembled within the valve seat, while a second side 64 is shown in a slightly flexed, sealed position, i.e. such that fluid flow is restricted or completely prevented. This is when the piston of the diaphragm is moving out of the chamber to which outlet valve 50 is mounted. The valve is in an open position when peripheral relief zone 60 is significantly flexed or lifted out of the seat to allow fluid flow. As shown in the figures, a cross-section of peripheral relief zone 60 comprises a stepped portion or a mathematical profile represented by a discrete or discontinuous function. However, this “stepped” design provides minimal flexural relief in that it only seals along an edge of lip 60, such that an effective sealing area 66 of valve 50 is limited to a thin line (as seen on side 64), creating sealing inconsistencies.
Furthermore, inconsistencies in the effective sealing area can be created during manufacturing the prior art valves. When molding the prior art valves, the molding die typically includes two halves. Where the two halves meet, there is the potential for flash, which is the material that is squeezed out at the parting line of the two halves. Referring to FIGS. 5B, 6B, this parting line 68, 70 is typically coextensive with the sealing edge of the lip of either the inlet valve or the outlet valve. This can cause an inconsistent sealing edge, and therefore an inconsistent seal.
In view of the issues of the prior diaphragm pumps, there remains a need for an improved cam/bearing assembly and an improved bearing/wobble plate assembly for improving the life and efficiency of the pump, without significantly increasing the time, complexity, and cost for manufacturing the pumps. Furthermore, there remains a need for an improved check valve design for improving the effective sealing characteristics of both inlet and outlet valves.